Marathon talks on ending the war in Ukraine have lasted through the night amid reports that the leaders involved are preparing to sign an agreement.
The leaders of Russia, Ukraine, France and Germany have been working to untangle a complicated web of military and political issues.
More than 5,300 people have died since April in the fighting between Ukrainian forces and Russia-backed separatists in two eastern provinces and the bloodshed has risen sharply in recent weeks.
Despite the talks, rebels and government troops reported fighting continuing across eastern Ukraine.
As US President Barack Obama considers rising calls at home for sending US lethal aid to Ukraine, European leaders fear that would only aggravate the fight.
Russia, meanwhile, faces a severe economic downturn driven in part by sanctions the West has imposed for supporting the separatists with troops and equipment, which Russia vehemently denies it is doing.
The urgency felt by all sides appeared to be underlined by the extraordinary length and discomfort of the talks between the leaders of Ukraine, Russia, France and Germany.
They sat down with each other last night in the Belarusian capital and the talks continued through the night as crowds of reporters waited anxiously for an outcome in a marble-floored, chandeliered convention hall in Minsk.
Officials have remained tight-lipped, praising progress but refusing to divulge details.
In a diplomatic blitz that began last week, German Chancellor Angela Merkel and French President Francois Hollande visited Kiev and Moscow to speak to Ukrainian President Petro Poroshenko and Russian President Vladimir Putin, paving the way for the marathon session in Minsk.
"The entire world is waiting to see whether the situation moves toward de-escalation, weapons pullback, ceasefire, or ... spins out of control," Mr Poroshenko said upon arriving.
Russian foreign minister Sergey Lavrov signalled some progress, saying the talks were "active, better than super". But it was unclear when a decision might be announced - and how soon the shooting would stop if an agreement is reached.
A top rebel official, Andrei Purgin, told Russian television that it might take a day or more for hostilities to end even if a ceasefire is called.